The present invention relates to propulsion systems in general, and more particularly to improvements in propulsion systems which can be utilized to transmit torque to the wheels of automotive vehicles or the like. Still more particularly, the invention relates to improvements in so-called flywheel propulsion systems wherein a flywheel can be used to receive torque from or to transmit torque to the output means of a power plant, such as an Otto engine or a diesel engine.
It is already known to equip a propulsion system for automotive vehicles or the like with a flywheel which can be connected to or disconnected from the crankshaft of the internal combustion engine by a suitable clutch and wherein the flywheel forms part of or cooperates with a combined starter-generator unit. The stator of the starter-generator unit is affixed to the housing of the engine and the rotor of such unit is connected with the flywheel. Reference may be had to German Pat. No. 932,334 which discloses a friction clutch interposed between the crankshaft of the engine and the flywheel, and wherein the rotor is affixed to the flywheel so as to rotate with reference to a stator which is attached to the housing of the internal combustion engine. Such starter-generator units are of particular advantage in propulsion systems of the type disclosed in U.S. Pat. No. 4,252,208 because they contribute to a substantial reduction of energy requirements of the power plant. Pat. No. 4,252,208 discloses a system wherein the engine can be arrested (i.e., the consumption of fuel terminated) during idling as well as under certain other circumstances, such as during coasting of the vehicle, i.e., whenever the engine is not required to transmit motive force to the front and/or rear wheels of the conveyance. The flywheel rotates due to inertia while the engine is brought to a halt. To this end, the propulsion system which is disclosed in U.S. Pat. No. 4,252,208 comprises a second clutch which is interposed between the input shaft of the change-speed transmission and the flywheel and is disengaged when the vehicle is coasting or when the engine is idling. The clutch between the flywheel and the crankshaft of the engine is engaged when the engine is to be started again; the flywheel then turns the crankshaft so as to set the engine in operation. The flywheel can rotate due to inertia for a relatively long interval of time (e.g., while the operator of the vehicle awaits the traffic signal to change from red or yellow to green) because both clutches can be disengaged during idling or coasting so that the flywheel can rotate independently of the engine crankshaft as well as independently of the input shaft of the transmission. The flywheel can be used to start the engine if the energy which is stored therein at the time the operator wishes to restart the engine suffices to turn the crankshaft at the speed and for an interval which is required to reestablish the operative condition of the power plant. Thus, all that is necessary to start the engine (while the flywheel still rotates at a sufficiently high speed) is to engage the clutch between the crankshaft and the flywheel. Once the engine is started, the clutch between the flywheel and the input shaft of the transmission is engaged to establish the flow of power from the engine to the parts (such as wheels) which receive torque from the output element or elements of the transmission.
In order to prevent excessive deceleration of the flywheel during the intervals of stoppage of the engine (e.g., during the aforementioned phase of operation of the vehicle which involves idling or coasting), the propulsion system of the type disclosed in U.S. Pat. No. 4,252,208 can be provided with a special starter motor whose purpose is to prevent the RPM of the flywheel from decreasing below a predetermined threshold value, i.e., an RPM which suffices to ensure reliable starting of the engine in response to engagement of the clutch between the crankshaft and the flywheel. The arrangement is such that the starter motor maintains the RPM of the flywheel within a certain range whose lower limit is the aforementioned threshold value. In heretofore known propulsion systems of the just outlined character, the starter motor transmits torque to the flywheel through the medium of a friction wheel which is movable into or from engagement with the flywheel, depending on the operating conditions, i.e., when the vehicle is arrested at an intersection or for other reasons or during coasting such as when the vehicle travels downhill and, consequently, the engine need not drive the wheels. A drawback of such mode of transmitting torque to the flywheel is that mechanical losses during frictional engagment between the friction wheel and the flywheel are relatively high. Moreover, the space requirements of the starter motor are substantial so that such motor cannot be readily installed in many types of automotive vehicles wherein, as a rule, the space below the hood is at a premium. Still further, the circuitry which is needed to establish or terminate the torque transmitting connection between the starter motor and the flywheel is complex, highly sensitive and expensive.
Applicants are further aware of U.S. Pat. No. 4,346,773. This patent discloses a coil-free rotor on the flywheel and a stator which is attached to a housing for two clutches one of which can connect the crankshaft of an internal combustion engine with the flywheel and the other of which can connect the flywheel with the input shaft of a change-speed transmission. The rotor of the propulsion system which is disclosed in this patent is not mounted on a component part of the clutch between the crankshaft of the engine and the flywheel.